Corrosion preventative



Nov. 19, 1940." H. s. POLIN 2,221,997

SORROS ION PREVENTAT IVE Filed Nov. 13, 1935 3 Sheets-Sheet 1 INVENTORHerberl S. P01 in ATTORNEYS Nov. 19, 1940. s PQLIN 2,221,997

CORROSION PREVENTAT IVE Filed Nov. 13, 1935 3 Sheets-Sheet 2 Q l sfilhmfib W i w 1 I l I I I l i lNVENTOR ATTORNEYS Herberl 5.1 066 Nov.19, 1940. H. s. POLIN 2,221,997

CORROSION PREVENTATIVE Filed Nov. 13, 1955 3 Sheets-Sheet 3 INVENTORHerbeni Slolin M M ll ORNEYS Patented Nov. 19, 1940 PATENT OFFICECORROSION PREVENTATIVE Herbert S. Polin, Sands Point, Long Island, N.Y., assignor of one-half to Harry A. F n-man,

Schenectady, N. Y.

Application November 13, 1935, Serial No; 49,500

Claims.

The present invention relates to method and apparatus for preventingcorrosion of metallic surfaces in contact with gaseous or liquid fluids.

In this case I claim the method or process of g performing the inventionset forth in my copending application Serial No. 701,976 for patent onCorrosion preventative filed December 12, 1933, which is now becomePatent No. 2,021,519, dated November 19, 1935. The claim of said patentis limited to the apparatus for practicing the said invention.

In accordance with accepted theory a nonhomogeneous metal in contactwith an electrolytic or ionizable solution constitutes a multiplicity ofsimple short circuited voltaic cells, wherein electronic currents flowwithin the metal from particles of the more reactive to particles of thenobler metal. Within the solution the converse is true, that is, theflow of electronic curgo rent is from the nobler to the more reactivemetal. The consequence is that the more reactive metal passes intosolution with liberation of hydrogen gas at the surfaces of the noblermetallic particles.

g; It has heretofore been proposed to overcome corrosion thus producedby suspending in the solution metallic bars, webs, or the like, betweenwhich and the metallic surface to be protected, a source of directvoltage is connected with its 30 negative electrode joined to theprotected metal.

The magnitude of the resultingv electronic current flowing within thesolution from the; protected metal to the suspended members is thenadjusted manually, according to the known prac- 35 tices, to equal orexceed thecorrodingelectronic" current, due to voltaic cell action,tending to flow into the more reactive portions of the protectedsurfaces, in consequence of which the more reactive metal is preventedfrom passing into solution and the protected surface maintained intact.

The difilculty with known methods wherein the compensating current flowis manually adjusted to offset the effect of the corroding current,resides in the fact that the latter vary in magnitude within wide limitsand more or less continuously due, for example, to temperature changes,fluctuations in strength of the electrolytic solution, etc. If thereforethe com- 50 pensating current is manually adjusted to equal thecorroding currents for a given instantaneous set of conditions,subsequent unbalances of one polarity will permit corrosion of theprotected surface to proceed, while unbalances of the opposite polaritywill entail consumption of the suspended bars or web members. Thus aftera period both the protected surface as well as the suspended memberswill be found badly corroded.

If, on the other hand, the compensating current is-establishecl of suchlarge magnitude as to more than counterbalance for all conditions theflow of corroding current, the suspended members will be completelyconsumed within such short intervals as to render this expedientimpracticable. 1

The present invention eliminates the defects noted by making adjustmentof the compensating current electrically automatic and such that thecompensating current can be caused to just balance the corroding currentfor all fortuitous 15 variations of the latter; or in the alternativethe compensating current can be made to vary automatically in responseto variations of the corroding current, but in such manner as alwaystoexceed the corroding current by a substantially constant amount. Thusthe present invention will assure complete and continuous protection ofthe metal to be preserved, while causing no consumption of the suspendedmembers, or a consumption thereof which can be made as gradual 5 as,desired. It will be appreciated that adjustment of the compensatingcurrent to more than counter-balance the corroding current constitutes,in a sense, a factor of safety assuring the elimination of all corrodingeffects in the protected surface.

Although not limited thereto, the invention is particularly applicableto the condensing apparatus used on lighter-than-air craft, in which themoisture content of the exhaust gases from the motors, is condensed soas to prevent, as far as possible, the lightening of the ship as fuel isburned. Since in airships any excess weight is undesirable, thecondensing pipes are made as thin as possible, and it has been foundthat these pipes are very rapidly corroded by the fuel exhaust gasescondensed, necessitating frequent replacement of the pipes.

This corrosion is due partly to the presence of carbon monoxide andcarbon dioxide in the ex- 4 haust gases, which in solution form acids,and,

. being in contact with the metallic condenser tubes, permitselectrolytic action to take place of the character above described,which is intensifled at the high temperatures of operation. Thecorrosion is in this instance also due to the fact that some or all ofthe molecules composing the exhaust gases, are electrically charged,whereby in the condensing process small electric currents are set upwhich additionally corrode the walls of the tube.

The present invention which compensates and hence eliminates both typesof corrosion, employs for maintaining the compensation electricallyautomatic, a space discharge device, such as an electronic tube havingan anode, a cathode and grid electrodes. The cathode system of the tubeis effectively grounded to the protected surface. Insulatedly suspendedin the electrolytic solution or in the exhaust gases are a pair ofconductive elements or screens, which may comprise concentriccylindrical meshes. The suspended elements are joined respectively toresistors interposed in the grid and anode circuits of the tube. Theconnections and electrical magnitudes are such that changes inconductivity or voltage developed within the fluid medium apply to thegrid of the tube instantaneous potentials of proper magnitude andpolarity to provide in its anode 'circuit the desired instantaneousvalue of compensation.

In the drawings: Fig. 1 shows diagrammatically a form of the inventionadapted to eliminate corrosion where the corroding currents are ofconstant polarity, either plus or minus, although susceptible tofluctuations in magnitude.

Fig. 2 shows an adaptation of the Fig. 1 arrangement to an extensiveconduit system to be protected.

Fig. 3 shows an arrangement employing a gaseous or glow discharge tubefor supplying relatively large compensating current where required.

Referring to Fig. 1, there is shown in longitudinal section a fluidconduit or container C, containing either a gaseous medium interspersedby charged particles, such as the exhaust gases of motors, or anelectrolytic medium, or both. Insulatedly mounted within the container,as by porcelain or ceramic supports 2, are a pair of conductive elementsor screens S and D, here shown as longitudinally spaced but which may beconcentric cylinders. Screen D is connected by means of a conductor 5through an insulating plug 6, to the grid G of an electronic tube V.

The cathode K, of the tube is energized from battery B1, through aresistor R, variably tapped through leak resistor L to the grid G oftube V, for biasing the grid as desired. The anode circuit of the tube,energized by battery B2, contains a potentiometer P, the midpoint M ofwhich is tapped by means of conductor 1 through an insulating plug 8 inthe container, to screen S therein. The container C to be protectedagainst corrosion, is variably tapped at T to potentiometer P by meansof conductor I0 containing an ammeter l-I.

Assuming container C to be filled with an electrolytic solution E,batteries Bi and B2 will establish in grid resistor L, with the systemas arranged in the drawings, an electronic current i1 flowing in thesolution from screen D to the container C returning over conductor 5.This current will be so small, due to the large value of the gridresistor L, as to produce no appreciable effect on meter H. Concurrentlythe space current of tube V will, in traversing the potentiometer P,establish a potential drop between points T and M thereof, producing anelectronic current i2 flowing from container C to screen S in thesolution.

It will be observed that current i: is in the right direction tocompensate or counterbalance the electronic current flowing into themore active metal portions of container C in consequence of the voltaiccell action described. For a. given set of conditions, conductivity ofthe solution, etc., current i2 can be so adjusted by variation ofpotentiometer tap T and by observation on meter I I, as to preventcorrosion of container C so long as the initial conditions remainunaltered.

Assume, however, that by some fortuitous circumstance the conductivityof solution l2 should increase, as by increase of temperature, increaseof concentration, etc. The resulting increase in corrosive voltaic cellaction established between the more and less active portions of thenonhomogeneous container C, immediately necessitates an increase in thecompensatory current i2, which is the result automatically produced bythe vacuum tube system as follows:

The increase in conductivity of solution E, decreases the totalresistance in the path traversed by the grid current ii, in consequenceof which current i1 increases thereby increasing the voltage drop acrossgrid resistor L, and thus increasing in a positive sense the biasingpotential applied to control grid G. This produces an increase of spaceor anode current in tube V, which in traversing the potentiometer P,increases the voltage between points T and M thereof, and henceincreases the magnitude of current i2 from container C to screen S,which is the result desired.

If on the other hand the conductivity of solution E should decrease, thecorroding currents would decrease and a smaller compensating current i2would suflice. The system of the drawings automatically provides forthis in a manner which is just the converse of that above described foran increase in conductivity of the solution. As the conductivity of thesolution decreases, the grid current i1 likewise decreases, therebydecreasing in a positive sense or increasing in a negative sense thebiasing potential applied to grid G. This decreases the space current oftube V, and hence the magnitude of the compensating current i2, whichagain is the result desired.

Therefore, irrespective of whether the conductivity of solution Eincreases or decreases from a given condition, the compensating currenti: will automatically vary in the same direction along with it, that iscurrent 1: always varies automatically in magnitude in the samedirection as do the forces tending to produce corrosion.

Now from a. series of preliminary tests based on the character ofelectrolyte or charged gaseous fluid normally present in container C,the metallic structure of the container as well as screens S and D,etc., the optimum value of current i2 for minimizing corrosion of allmetallic surfaces, can be ascertained for various conductivities of thefluid. With this information preliminarily available, the system can beso designed as automatically to maintain the current 1': at its optimumvalue throughout the range of fluid conductivities encountered inpractice. Factors determinative of this design are the resistances of Land potentiometer P, the magnitude of batteries B1 and B2,characteristics of tube V, etc. By suitably proportioning these circuitcomponents the current i2 can not only be made to vary automatically inthe right direction but by just the proper amount to effect optimumcompensation for each change in conductivity of the fluid.

Where, as in the case of condensation of exhaust gases from motors,charged particles of the gaseous medium tend, in discharging to thegrounded pipe I, to set up a flow of corroding current to or from thepipe, optimum compensation may be effected by so adjusting thecompensating current i2 th9,t. the meter deflection is zero, since forthis adjustment the compensating current would be equal and opposite tothe corroding current. It will be observed in this connection that iffound necessary, the polarity of the compensating current i2 can bereversed in-sign as well as adjusted in magnitude by merely shifting thevariabletap T to one side or the other of the mid- E I.ffIl'iefinvention is not limited to a single tube V for providing theautomatically regulated compensating current or voltage. It may beadvisable in"certain' cases to arrange additional tubes in tandem withtube V, in which event the potentigmeter P would be interposed in theanode circhit of ag'subsaquent tube, tube V merely serving tocontinuously detect the requisite electrical characteristic of fluid E,and to control in accordance therewith the voltage applied to asubsequent tube, which in turn would provide the proper compensatingvoltage or current.

In this connection the employment of a plurality of tubes in tandemprovides a means alternative to the mid-tap M of potentiometer P forreversing the polarity of the compensating voltage. Thus the midtap Mcould conveniently be shifted to the lower terminal of thepotentiometer.

In the case of a large ship, complex relationships, electro-potentially,between the various pipes, the hull, the sea water and stray electricalcurrents leaking from the electrical conduits, may impart to themetallic structure a multiplicity of currents varying in sign, potentialand magnitude at any moment. 'Ijhe system herein described provides forthe installation of a detecting and distribution panel identified withan electrical network throughout the ship, and with a central powersupply located at the distribution panel so introduced into each circuitas to effectively neutralize the many and variable currents flowing atthose points located as major potential difference sources. The area ofefiectiveness of each neutralizing circuit may be determined by themetallurgical bulk of this branch, by the areaof the source of potentialdifference, and by the proximity of the neutralizing system to eachsource.

Fig. 2 shows the manner of adapting the invention to a continuousconduit system traversed by a fluid medium of corrosive character. Theconduit system, which may represent the sea water damage control mainsof a battleship, etc., comprises pipe sections C1, C2, Ca, etc. Atappropriate intervals, as best determined by tests on the particularsystem under consideration, are

insulatedly positioned in the fluid medium, the screens S1. S2, S3,connected to potentiometers P1, P2, P3, etc., arranged in the anodecircuits of tubes V1, V2, V3, etc. in the manner of Fig. l. Concentricwith screens S1, S2, Sc, etc., respectively, or appropriately spacedtherefrom, are the detector screens D1, D2, D3, etc., joined to thegrids of tubes V1, V2, V3 respectively. All of the tubes are energizedfrom the common filament and space current supply sources B1 and B2, asshown. In the operation of the system the variable arms of thepotentiometers P are individually adjusted to eliminate corrosion in theparticular pipe section containing the associated screens S and D.

The circuit of Fig. 3 is ideally adapted to prevent corrosion inextensive conduit systems, such as the sea water ballast pipe lines ofbattleships, wherein the total current required for purposes ofcompensating the corroding currents, is relatively large, and may beconsiderably in excess of that which can be conveniently supplied by thespace current of an electronic tube- Under such circumstances resort maybe had to gaseous or glow discharge tubes, such for example as thatknown as the Thyratron, for providing the compensating current.

In the circuit of Fig. 3 the corroding potentials are detectedthermionically by means of the electronic tube V1 having its grid G1connected, through short circuiting contacts of a switch 25 to theconduit C, and its cathode connected to detector screen D positioned inthe fiuid medium E within the conduit.

If the fluid E comprises an electrically charged gaseous medium, a.potential will be established on grid G1 determined by the polarity andmagnitude of the charge existing between screen D and the conduit C. Ifon the other hand the fluid is an ionized liquid, switch 25 may beoperated to connect the battery 26 in the grid circuit, in order toestablish a current flow in the resistor L1, the voltage drop acrosswhich will depend upon the conductivity of the electrolyte.

In any event the corroding forces thus detected establish, by variationin the space path resistance of tube V1 automatic regulation of a gridcontrolled, glow discharge tube V2, such that a compensating current iscaused to flow between screen S and conduit C which varies in conformitywith the corroding forces.

As is well known, the operation of grid controlled gaseous dischargetubes necessitates periodically interrupting the flow of space currentin orderto maintain operation of the device under control of its grid.To this end tube V2 is energized from an alternating current source 21connected to a transformer 28 having secondary windings 30 and 3|, theone for energizing the cathode K2, and the other for applying analternating potential between the cathode K2 and the anode A2.

The magnitude of space current supplied-by tube V2 is regulated undercontrol of tube V1 by connecting its grid G2 through the variableresistance consisting of potentiometer P1 in shunt to the space pathresistance of tube V1, and thence to cathode K2 through a secondarywinding 29 of transformer 28. An inductance 33 is connected between gridG2 and anode A2. With the elements properly proportioned, variation inthe space path resistance of tube V1 inresponse to variations in itsgrid potential, produces a relative shift in phase of alternatingcurrent applied between grid and cathode of tube V2 with respect to thatapplied between its anode and cathode such as to vary in the mannerrequired for automatic compensation the average space current of tubeV2.

Connected in the anode circuit of tube V2 is a low pass filter 32 theoutput of which terminates in a potentiometer P2 variably tapped at T2to screen S, with the positive terminal of potentiometer connected toconduit C.

The rectified pulsating current flowing between anode and cathode oftube V2 is thus converted by the filter 32 into a non-pulsating directcurrent traversing potentiometer P2, thereby providing the requisiteflow of compensating current between screen S and conduit 0.

What I claim is:

l. The method of preventing corrosion of a metal subjected toelectrolytic action of the fluid which comprises, continuously detectingthe potential difference between the metal and the fluid, utilizing thedetected potential difference for controlling and varying aspacedischarge current, causing said space discharge current to apply acompensating voltage between the metal and the fluid in opposition tothe detected potential difference, whereby the potential differencetending to produce corroding currents is continuously counterbalanced bythe compensating voltage.

2. Means preventing corrosion of a metal surface subjected toelectrolytic action of the fluid comprising, a pair of metallic membersinsulatedly positioned in said fluid, a space discharge device having ananode, a cathode and a control electrode, means responsive to spacecurrent of said tube and including one said metallic member for passingthrough said surface a compensating current of opposite polarity to thecurrent causing corrosion, and means including the second said metallicmember and said control electrode for automatically varying thecompensating current to continuously counterbalance variations of thecorroding current.

3. Means preventing corrosion of a metallic surface subjected toelectrolytic action of a fluid comprising, a pair of metallic membersinsulatedly positioned in said fluid, a space discharge device having ananode, a cathode and a control electrode, means responsive to spacecurrent of said tube for applying between the metallic surface and onesaid metallic member a compensating voltage in opposition to the voltagetending to cause corrosion, and means including the second said metallicmember and said control electrode for automatically so varying thecompensating voltage as to continuously counterbalance the voltagetending to cause corrosion.

4. Means preventing corrosion of a metallic surface subjected toelectrolytic action of a fluid comprising, a pair of metallic screensinsulatedly positioned in said fluid, a thermionic tube having an anode,a cathode and a grid electrode, an energizing connection between saidanode and cathode, potentiometric means interposed in said connectionfor impressing between the metallic surface and one said screen acompensating voltage of opposite polarity to the voltage tending tocause corrosion, and means including a resistance between said grid andcathode and a connection therefrom to said second screen forautomatically so varying the compensating voltage as continuously tocounterbalance the voltage tending to cause corrosion.

5. Means preventing corrosion of a metallic surface subjected toelectrolytic action of a fluid comprising, a pair of metallic screensinsulatedly positioned in said fluid, a thermionic tube having an anode,a cathode and a grid electrode, an energizing connection between saidanode and cathode, potentiometric means interposed in said connectionfor passing between the metallic surface and one said screen acompensating current of opposite polarity to the current causingcorrosion, and means including a resistance between said grid andcathode and a connection therefrom to said second screen forautomatically so varying the compensating current as continuously tocounterbalance the currents causing corrosion.

HERBERT S. POLIN. V

